OBJECTIVE: The overall goal of this ongoing project is to investigate the role of endothelin-1 (ET-1) in human lung injury. HYPOTHESES: 1. During dysregulated inflammatory events, we hypothesize that inflammatory mediators, changes in O/2 tension, and alterations in second messengers lead to an increase in ET-1 production and ET receptor expression in human lung cells. 2. We hypothesize that ET-1 produces lung injury by increasing endothelial cell susceptibility to oxidant damage and by enhancing PMN-mediated injury. 3. We hypothesize that increased levels of ET-1 and increased expression of ET receptors promote alveolar inflammation and pulmonary hypertension in patients with ARDS. RESEARCH PLAN: The project will investigate molecular, biochemical and physiologic mechanisms by which the ET system (ET-1 and ET receptors) influences lung injury. The first aim will investigate the molecular and cellular regulation of ET-1 synthesis and ET receptors in human lung endothelial cells, epithelial cells and macrophages in response to inflammatory modulators and physiologic conditions (hypoxia and hyperoxia) present in ARDS patients. These cells have been selected because, in ARDS lungs compared to non-ARDS lungs, these cells have a marked increased in ET-1 immunostaining. The second aim will determine the effect of ET on injury in pulmonary endothelial cells, vascular tissue, the isolated lung and the whole animal. These experiments will test the hypothesis that ET produces injury by increasing endothelial cell susceptibility to oxidant injury and by promoting neutrophil-mediated damage. These experiments will extend our preliminary findings, which indicate that ET promotes injury, and will focus on investigating potential mechanisms. The third aim will compare the level of ET-1 production and ET receptor expression in the lungs of ARDS and at risk patients and assess the relationship between plasma and bronchoalveolar lavage ET-1 levels and pulmonary hypertension, markers of alveolar inflammation and clinical course. This aim will investigate the hypothesis that ET contributes to alveolar inflammation and pulmonary hypertension in ARDS patients. SIGNIFICANCE: The proposed research will substantially improve our understanding of the role of ET-1 in human lung injury and the mechanism by which ET-1 promotes vascular injury and inflammation.